Gasification is a process used to convert carbonaceous materials, such as coal, petroleum, or biomass into predominantly carbon monoxide and hydrogen (syngas) by reacting the carbonaceous material at high temperatures. Syngas may be burned directly in internal combustion engines, used to produce methanol and hydrogen, or converted via the Fischer-Tropsch process to synthetic fuels.
A wide variety of carbon-containing materials can be used as a feedstock for gasification, including biomass and plastic waste. Gasification has the potential to be an important technology for renewable energy and is generally carbon neutral. U.S. Pat. No. 6,767,375 teaches a biomass gasifier reactor for producing syngas. The biomass gasifier includes a helical coil disposed concentrically in a reactor vessel having a burner positioned at the bottom of the vessel and a generally cylindrical heat shield having a truncated conical section with the bottom of the cylinder closed at the end toward the burner.
U.S. Pat. No. 7,228,806 teaches a biomass gasification system comprised of a primary combustion chamber, a rotating grate within the primary combustion chamber for supporting the biomass during gasification, a feeder unit in communication with the primary combustion chamber, a secondary combustion chamber, an oxygen mixer, and a heat exchanger and an exhaust stack. Also, U.S. Pat. No. 6,972,114 teaches a biomass gasifier and method for producing low BTU gas while removing char and ash.
United States Patent Application No. 2008/0216405 teaches carbonization and gasification of biomass wherein the biomass is first carbonized, and the resulting char and pyrolysis gas fed respectively to a high temperature gasifying step and to a gas reformer. This helps maintain the temperature required to avoid tar formation in the gas reformer stage.
Biomass gasification carries significant energy debits compared to coal and petroleum based feed materials due to its relatively low carbon content. Gasification reactions are complicated by the presence of relatively high oxygen levels, resulting in a significant amount of CO2 in the product synthesis gas. Most biomass gasifiers currently in use, or under commercial development, operate at relatively low pressures (<100 psig) in order to achieve the desired thermal flux necessary to achieve high gasification yields while minimizing the formation of undesired tar and soot.
Since gasification is an endothermic reaction, heat must be supplied either indirectly through exchange with a hot heat transfer surface, or directly by the simultaneous heat release associated with partial oxidation resulting from the introduction of oxygen-containing gas into the reactor. Most biomass contains significant amounts of inorganic material (i.e. silica, potassium and other elements) which do not undergo gasification and which can agglomerate and fuse into a phase commonly referred to as slag when exposed to elevated temperatures (typically >1800° F.). Gasifiers that are designed to minimize slag formation, and use partial oxidation to generate the required thermal energy for gasification (directly heated gasifiers), must control the addition of oxygen in order to avoid excessive temperatures within the partial oxidation zone.
While there is significant activity in the field of converting biomass to fuel products using gasification, there is still a need in the art for improved and more efficient processes for achieving same.